1. Field of the Invention
The present invention relates to an auxiliary device for a machine tool for supporting a workpiece to be machined by the machine tool.
2. Description of the Related Art
In surface-finishing a workpiece W having a hollow portion, as shown in FIGS. 3A, 3B or 3C, the workpiece W is ground. A tool with a shaft, as illustrated in FIG. 4, is used for grinding the workpiece W. Diamond abrasive grains are deposited at the tip end of the tool T. As depicted in FIG. 5, the tool T abuts against the inner surface of the workpiece W while rotating at a high speed, thereby realizing internal grinding of the workpiece W.
It is known that, in the above mentioned surface finish, if the tool T is reciprocated in the axial direction, indicated by a double-headed arrow D in FIG. 5 (this type of machining is hereinafter referred to as "oscillation-machining"), surface roughness can be reduced as well as machining efficiency can be enhanced. The reciprocation of the tool T is performed at about 100 cycle/min. The width of the reciprocation of the tool T is limited within the range where the diamond abrasive grains deposited in the tool T can be brought into contact with the surface of the workpiece W to be machined from the upper end to the lower end thereof.
Conventionally, a special machine tool such as an internal grinding machine or a jig grinding machine is used for the oscillation machining. The internal grinding machine or jig grinding machine has an oscillation function for reciprocating the tool T in the axial direction. Accordingly, the surface finishing of the workpiece W, using the internal grinding machine or jig grinding machine, can sufficiently reduce the surface roughness of the workpiece W. However, since the internal grinding machine or jig grinding machine is manufactured to correspond to the shape of the workpiece W to be machined, the internal grinding machine or jig grinding machine is very expensive and, further, it is not generally compatible with a popular multi-tool machining center and numerical control milling machine. Consequently, oscillation machining using the internal grinding machine or jig grinding machine is expensive.